ᐅ Moisture Levels in New Buildings Increase During Wet Weather – Experiences?

Hello,

I am a tenant and recently moved into a newly built apartment, where, as in my previous home, I set up a hygrometer. While the humidity in my previous apartment mostly stayed around 40-45%, which was rather dry, in the new apartment it sometimes ranges from 40-55%, but during wet weather it remains consistently between 60 and 70%. The strange thing is that the humidity inside only rises this much during wet weather and then does not drop again until the weather changes.

There is effective cross-ventilation every morning and evening, with a full air exchange. Over the course of the first “wet day,” meaning about 12 to 14 hours, the humidity rises significantly, even though practically no moisture is generated indoors and the apartment is actually quite large. If the weather stays humid, the apartment remains damp for days until the weather improves.

Currently, I’m not quite sure why this happens or if I am doing something wrong or could do better. In any case, anything above 60% humidity in living and working spaces is far from comfortable and, of course, promotes mold growth. Right now, the humidity is actually a solid 70%. Since I’m a tenant, I do have a relatively easy way out if this really turns out to be a serious problem. What’s strange to me is that there is no ventilation system at all. However, I lack the technical knowledge overall. Does anyone here have experience and can offer advice?

Thank you!

riverstorm schrieb:

Effective cross-ventilation is done every morning and evening, allowing a complete air exchange. Over the first "wet day," meaning about 12 to 14 hours, humidity increases significantly, even though almost no moisture is generated indoors and the apartment is actually oversized. If the weather remains damp, the apartment will also stay humid for several days until the weather improves.

- You are ventilating too little.
- If the outdoor air is moist, it is difficult for the indoor air to become drier unless heating is used.
- A newly built house remains somewhat damp for 2 to 3 years, which is normal.

Good morning,

Basically, it is quite normal to have relatively high humidity levels in a newly built house. This is because, during the construction phase—especially during interior finishing works like plastering and screeding—a lot of moisture is introduced into the building. At the same time, the house is built very airtight, so this moisture has little chance to leave the building. This is further intensified nowadays by fast construction schedules and additives that accelerate curing and drying.

Now, regarding your specific case:

Besides humidity, I would also be interested in the temperature. These two factors always go hand in hand. Cold air can hold less moisture, which means relative humidity increases as temperature drops. Furthermore, the cold and wet outside conditions we often have right now are not favorable for drying the building because even when ventilating abruptly (also called “shock ventilation”), the incoming air is already nearly saturated and thus cannot absorb much moisture from inside.

So, it is not surprising that you are experiencing this, but the values are quite high. Perhaps the building was occupied a bit too soon, or finished and heated late during this very damp winter (which made it difficult for the water to escape).

As for the ventilation system, no general statement can be made. New buildings must have a regulated, continuous minimal air exchange. This is usually achieved through external inlets in the walls or windows. If the apartment has many windows, sometimes so-called trickle vents (small vents in window frames visible only when the window is open) are sufficient. However, this airflow is by no means enough to dry out your apartment and does not replace regular manual ventilation by tenants. This mainly serves as a protective function when tenants change or when the apartment is vacant for a longer period.

Now, my reply might still not have solved your problem...

1. Continue ventilating regularly with full window openings—ventilation in tilt position (“tilt ventilation”) actually promotes mold growth above window lintels.
2. Keep the apartment warm (and then ventilate even more).
3. If the problem persists, contact your landlord and possibly arrange for condensate dehumidifiers to be installed, which can run while you are away (they tend to be quite intrusive when you are at home).
4. If water condenses on the windows, wipe it off.

Best regards,
Jann

Humidity should always be assessed in relation to temperature, including room temperature and wall temperatures.

Up to 70% humidity is generally not a problem. Beyond that, it becomes uncomfortable, and at 85% it is considered damp.

The ideal range is 50 to 60%.

Thanks for the many quick responses!
The temperature is currently quite warm, around 23 to 24 degrees Celsius (73 to 75°F), in my opinion. I’m still not sure what is causing this.

Ventilating more often is unfortunately a bit difficult since I’m usually not home during the day. However, this was always perfectly sufficient in my previous apartments (including two first occupancies), and nowhere else could I create such an effective cross breeze as here.
Regarding continuous ventilation, there really isn’t anything—no air vents at all. The apartment is practically sealed airtight when the windows are closed (is this even allowed for a building constructed in 2020/2021?).

If this doesn’t sound too unusual, I’ll probably get a dehumidifier. However, I’m still surprised that this problem only occurs during or after wet weather(?).

Regarding whether this is allowed, you would need to review the calculations.
Your minimum air exchange rate is required, which is calculated based on DIN 1946-6 considering various factors.
If this rate is not achieved through the normal structural conditions, appropriate systems must be installed.
As a user, it is therefore not immediately clear to you whether this can be correct or incorrect.
However, my experience shows that structural measures are usually necessary, as buildings tend to be very airtight and well insulated.

The problem with damp / cold weather is that ventilating on such days hardly has any benefit. That is why humidity increases, because less moisture is removed, while walls and floors continue to release moisture into the warm indoor air.

A dehumidifier is definitely a good initial investment. But don’t expect too much. In my home, it has helped in the sense that I no longer have damp windows in the bathroom during winter (building with only moderate energy efficiency).